Purging of Fiber Optic Conduits in Subterranean Wells

ABSTRACT

Purging of fiber optic conduits in subterranean wells. A downhole optical sensing system includes an optical line, at least two tubular conduits, one conduit being positioned within the other conduit, and the optical line being positioned within at least one of the conduits, and a purging medium flowed in one direction through one conduit, and flowed in an opposite direction between the conduits. A method of purging a downhole optical sensing system includes the steps of: installing at least two conduits and an optical line in a well as part of the sensing system, one conduit being positioned within the other conduit, and the optical line being positioned within at least one of the conduits; and flowing a purging medium through the conduits in the well, so that the purging medium flows in one direction through one conduit and in an opposite direction between the conduits.

CROSS-REFERENCE TO RELATED APPLICATION

The present application claims the benefit under 35 USC §119 of the filing date of International Application No. PCT/US07/89000, filed Dec. 28, 2007. The entire disclosure of this prior application is incorporated herein by this reference.

BACKGROUND

The present invention relates generally to equipment utilized and operations performed in conjunction with subterranean wells and, in an embodiment described herein, more particularly provides for purging of fiber optic conduits in subterranean wells.

It is very important for optical fibers to be well protected when they are used in harsh, hostile environments. For example, in high temperature environments, such as in steam injection wells or other high temperature well environments, there are a variety of possibly damaging effects to guard against.

One effect of high temperature environments on optical fibers is accelerated hydrogen darkening. In some cases, an optical fiber can become unusable due to hydrogen darkening within a few days of its installation.

Therefore, it will be appreciated that improvements are needed in the art of protecting optical fibers in hostile environments.

SUMMARY

In carrying out the principles of the present invention, a downhole optical sensing system and associated method are provided which solve at least one problem in the art. One example is described below in which an optical fiber is installed within coaxial conduits for convenient purging of hydrogen from about the optical fiber. Another example is described below in which a purging medium is circulated downhole and returned from downhole via the coaxial conduits.

In one aspect, a downhole optical sensing system is provided. The system includes at least one optical line and at least two tubular conduits. One conduit is positioned within the other conduit. The optical line is positioned within at least one of the conduits. A purging medium is flowed in one direction through one conduit, and is flowed in an opposite direction between the conduits.

In another aspect, a method of purging a downhole optical sensing system is provided. The method includes the steps of: installing at least two conduits and an optical line in a well as part of the sensing system, one conduit being positioned within the other conduit, and the optical line being positioned within at least one of the conduits; and flowing a purging medium through the conduits in the well, so that the purging medium flows in one direction through one conduit and in an opposite direction between the conduits.

These and other features, advantages, benefits and objects will become apparent to one of ordinary skill in the art upon careful consideration of the detailed description of representative embodiments of the invention hereinbelow and the accompanying drawings, in which similar elements are indicated in the various figures using the same reference numbers.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic partially cross-sectional view of a system and method embodying principles of the present invention;

FIG. 2 is an enlarged scale schematic partially cross-sectional view of the optical sensing system;

FIG. 3 is a schematic partially cross-sectional view of a method of purging the optical sensing system; and

FIG. 4 is a schematic partially cross-sectional view of an alternate method of purging the optical sensing system.

DETAILED DESCRIPTION

It is to be understood that the various embodiments of the present invention described herein may be utilized in various orientations, such as inclined, inverted, horizontal, vertical, etc., and in various configurations, without departing from the principles of the present invention. The embodiments are described merely as examples of useful applications of the principles of the invention, which is not limited to any specific details of these embodiments.

In the following description of the representative embodiments of the invention, directional terms, such as “above”, “below”, “upper”, “lower”, etc., are used for convenience in referring to the accompanying drawings. In general, “above”, “upper”, “upward” and similar terms refer to a direction toward the earth's surface along a wellbore, and “below”, “lower”, “downward” and similar terms refer to a direction away from the earth's surface along the wellbore.

Representatively illustrated in FIG. 1 is an optical sensing system 10 and associated method which embody principles of the present invention. The system 10 in this example is used to sense fluid properties or other parameters in a wellbore 12. However, the principles of the invention may be used for other purposes, as well.

As depicted in FIG. 1, a production tubing string 14 has been installed in the wellbore 12. Attached to the tubing string 14 during installation is a conduit assembly 16 and a sensor 18. The conduit assembly 16 and sensor 18 may be separately attached to the tubing string 14 (for example, using clamps, etc.), or the conduit assembly and/or the sensor 18 could be integrally formed with the tubing string 14.

As another alternative, the conduit assembly 16 and/or sensor 18 could be installed in the wellbore 12 whether or not the tubing string 14 is also installed in the wellbore. Therefore, it should be clearly understood that the principles of the invention are not limited in any way to the details of the system 10 illustrated in the drawings or described herein.

Referring additionally now to FIG. 2, an enlarged scale cross-sectional view of a portion of the system 10 is representatively illustrated. In this view it may be seen that the conduit assembly 16 includes an inner conduit 20 and an outer conduit 22.

Multiple optical waveguides or lines 24, 26, 28 are contained within the conduits 20, 22. Although three lines 24, 26, 28 are depicted in FIG. 2, any number of optical lines (including one) may be used. The lines 24, 26, 28 may be of the type known as optical fibers or any other type of optical waveguide.

In addition, any number of conduits may be used. Although the conduit 20 is described for convenience herein as an “inner” conduit, another conduit could be contained within the conduit 20, and although the conduit 22 is described for convenience herein as an “outer” conduit, another conduit could be external to the conduit 22. The conduits 20, 22 may be made of any suitable material, such as stainless steel, polymers, composites, etc.

The optical lines 24, 26 are preferably used for distributed temperature sensing (DTS), a technique well known to those skilled in the art, in which backscattered light is analyzed to determine the temperature distribution along optical lines or fibers. In this manner, the lines 24, 26 themselves comprise temperature sensors in the optical sensing system 10.

The optical line 28 is preferably operatively connected to the sensor 18 (for example, via a fusion splice 30). The sensor 18 could be a sensor designed to detect a property at a single location, such as a pressure sensor. The sensor 18 could be an optical sensor (such as the pressure sensor described in U.S. Pat. No. 7,159,468), or it could be another type of sensor.

The splice 30 is preferably contained within a chamber 32. The chamber 32 is preferably connected between the sensor 18 and a lower end of the conduit assembly 16, for example, using pressure isolating fittings 34 at either end of a tubular housing 36. However, other arrangements and configurations may be used in keeping with the principles of the invention.

In the example of FIG. 2, a conventional 180-degree turnaround 38 in the chamber 32 is operatively connected to the lines 24, 26, so that the lines and the turnaround form a continuous optical waveguide from a remote location (such as the earth's surface) to a downhole location, and back to the remote location. This arrangement permits more accurate double-ended (as opposed to single-ended) distributed temperature measurements to be obtained using the lines 24, 26.

An acceptable turnaround for use in the system 10 is manufactured by AFL Telecommunications LLC of Duncan, S.C. USA. Fusion splices (such as the fusion splice 30) may be used to connect the lines 24, 26 to the turnaround 38.

In one beneficial feature of the system 10, the chamber 32 is in communication with the interior of the inner conduit 20, and in communication with the space 40 between the conduits 20, 22. In this manner, a continuous flow passage is formed from the remote location (such as the earth's surface, sea floor, etc.) to the downhole location at the chamber 32, and back to the remote location.

This configuration permits a purging medium 42 (see FIGS. 3 & 4) to be flowed in one direction downhole, and flow in an opposite direction uphole, in order to purge hydrogen from about the lines 24, 26, 28. For example, the purging medium 42 could comprise gas (such as nitrogen or another inert gas, air, etc.), a liquid, gel, etc. The purging medium 42 could have hydrogen scavenging capability.

Referring additionally now to FIG. 3, one method of purging the hydrogen from about the lines 24, 26, 28 in the conduit assembly 16 is representatively illustrated. This method utilizes a purging device 44 connected to an upper end of the conduit assembly 16 at the remote location.

The purging medium 42 is flowed via a conduit 46 into an interior chamber 48 of the device 44. The chamber 48 is in communication with the space 40 between the conduits 20, 22. Thus, the purging medium 42 flows downhole through the space 40 between the conduits 20, 22, into the chamber 32 at the lower end of the conduit assembly 16, and then back uphole to the remote location via the interior of the inner conduit 20. In this manner, hydrogen is purged from about the lines 24, 26, 28 in the conduit assembly 16.

Referring additionally now to FIG. 4, another method of purging the hydrogen from about the lines 24, 26, 28 in the conduit assembly 16 is representatively illustrated. This method utilizes a somewhat differently configured purging device 50 connected to an upper end of the conduit assembly 16 at the remote location.

The purging medium 42 is flowed via the conduit 46 into an interior chamber 52 of the device 50. The chamber 52 is in communication with the interior of the conduit 20. Thus, the purging medium 42 flows downhole through the interior of the inner conduit 20, into the chamber 32 at the lower end of the conduit assembly 16, and then back uphole to the remote location via the space 40 between the conduits 20, 22. In this manner, hydrogen is purged from about the lines 24, 26, 28 in the conduit assembly 16.

It may now be fully appreciated that the above description of representative examples of the system 10 and associated methods provide important advancements in the art of protecting optical lines from damage in harsh, hostile environments. In particular, the system 10 and methods described above enable convenient, efficient and inexpensive purging of conduits 20, 22 in order to protect the lines 24, 26, 28 from hydrogen darkening. Other uses may be made of the system 10 and methods in keeping with the principles of the invention.

Described above is a downhole optical sensing system 10 which includes at least one optical line 24, 26, 28 and at least two tubular conduits 20, 22. One conduit 20 is positioned within the other conduit 22. The optical line 24, 26, 28 is positioned within at least one of the conduits 20, 22. A purging medium 42 is flowed in one direction through one conduit 20, and flowed in an opposite direction between the conduits 20, 22.

The optical line 28 may be operatively connected to a downhole sensor 18. The optical lines 24, 26 may comprise a downhole sensor. The optical lines 24, 26, 28 may be positioned within the inner conduit 20.

The purging medium 42 may comprise a gas. The purging medium 42 may comprise a hydrogen scavenging medium.

The purging medium 42 may be flowed downhole in a first direction and return uphole in a second direction. The purging medium 42 may be flowed downhole in the second direction and return uphole in the first direction.

The system 10 may also include a downhole chamber 32 in fluid communication with an interior of the inner conduit 20 and an annular space 40 between the conduits 20, 22. The system 10 can include a 180-degree turnaround in the optical lines 24, 26 within the downhole chamber 32.

Also described above is a method of purging a downhole optical sensing system 10. The method includes the steps of: installing at least two conduits 20, 22 and at least one optical line 24, 26, 28 in a well as part of the sensing system 10, one conduit 20 being positioned within the other conduit 22, and the optical line 24, 26, 28 being positioned within at least one of the conduits; and flowing a purging medium 42 through the conduits in the well, so that the purging medium flows in one direction through one conduit 20 and in an opposite direction between the conduits 20, 22.

The method may include operatively connecting the optical line 28 to a downhole sensor 18. The method may include utilizing the optical line 24, 26 as a downhole sensor.

The method may include flowing the purging medium 42 downhole in one direction and returning the purging medium from downhole in the opposite direction. The method may include flowing the purging medium 42 downhole in the second direction and returning the purging medium from downhole in the first direction.

Of course, a person skilled in the art would, upon a careful consideration of the above description of representative embodiments of the invention, readily appreciate that many modifications, additions, substitutions, deletions, and other changes may be made to the specific embodiments, and such changes are contemplated by the principles of the present invention. Accordingly, the foregoing detailed description is to be clearly understood as being given by way of illustration and example only, the spirit and scope of the present invention being limited solely by the appended claims and their equivalents. 

1. A downhole optical sensing system, comprising: at least one optical line; at least first and second tubular conduits, the first conduit being positioned within the second conduit, and the optical line being positioned within at least one of the first and second conduits; and a purging medium flowed in a first direction through the first conduit, and flowed in a second direction opposite to the first direction between the first and second conduits.
 2. The system of claim 1, wherein the optical line is operatively connected to a downhole sensor.
 3. The system of claim 1, wherein the optical line comprises a downhole sensor.
 4. The system of claim 1, wherein the optical line is positioned within the first conduit.
 5. The system of claim 1, wherein the purging medium comprises a gas.
 6. The system of claim 1, wherein the purging medium comprises a hydrogen scavenging medium.
 7. The system of claim 1, wherein the purging medium is flowed downhole in the first direction and returns in the second direction.
 8. The system of claim 1, wherein the purging medium is flowed downhole in the second direction and returns in the first direction.
 9. The system of claim 1, further comprising a downhole chamber in fluid communication with an interior of the first conduit and an annular space between the first and second conduits.
 10. The system of claim 9, further comprising a 180-degree turnaround in the optical line within the downhole chamber.
 11. A method of purging a downhole optical sensing system, the method comprising the steps of: installing at least first and second conduits and at least one optical line in a well as part of the sensing system, the first conduit being positioned within the second conduit, and the optical line being positioned within at least one of the first and second conduits; and flowing a purging medium through the first and second conduits in the well, so that the purging medium flows in a first direction through the first conduit and in a second direction opposite to the first direction between the first and second conduits.
 12. The method of claim 11, wherein the installing step further comprises operatively connecting the optical line to a downhole sensor.
 13. The method of claim 11, further comprising the step of utilizing the optical line as a downhole sensor.
 14. The method of claim 11, wherein the installing step further comprises positioning the optical line within the first conduit.
 15. The method of claim 11, wherein the purging medium comprises a gas.
 16. The method of claim 11, wherein the purging medium comprises a hydrogen scavenging medium.
 17. The method of claim 11, wherein the purging medium flowing step further comprises flowing the purging medium downhole in the first direction and returning the purging medium from downhole in the second direction.
 18. The method of claim 11, wherein the purging medium flowing step further comprises flowing the purging medium downhole in the second direction and returning the purging medium from downhole in the first direction.
 19. The method of claim 11, wherein the installing step further comprises connecting a downhole chamber in fluid communication with an interior of the first conduit and an annular space between the first and second conduits.
 20. The method of claim 19, wherein the installing step further comprises providing a 180-degree turnaround in the optical line within the downhole chamber. 